Surface fall applied fertilizer has been shown to remain in the soil and is available for plant uptake for all crop types.
Nitrogen is a significant component of proteins which are essential for growth. Nitrogen must be in the root zone and available for uptake as crops enter into their rapid growth period. Therefor nitrogen availability for plant use is essential for crop growth and yields.
There are three main ways in which nitrogen may be lost from your soil;
- Ammonia Volatilization – Volatilization is the process in which a dissolved sample is vaporized. With regards to nitrogen, the loss occurs when the soil urease enzymes breaks the urea molecule into ammonia gas. This occurs through the process of hydrolysis, a hydrogen ion is consumed raising the soil pH level around the urea. Nitrogen in the soil moves towards ammonia at high pH levels, putting shallow banded or surface applied urea at risk of loss through volatilisation. If volatilisation happens, as much as 30 to 50% of the nitrogen that is not incorporated into the soil could be lost as ammonia gas through the porous layers of the topsoil. This can occur in all soil types.
- Denitrification – Nitrogen loss occurs when nitrate nitrogen is converted back to the gaseous form. Nitrogen diffuses out of the soil and is lost into the atmosphere. This occurs in soils that are poorly drained or become water logged.
- Nitrate leaching – Nitrate is moved below the plant’s root zone by percolating water. Leaching is most common in sandy soils.
Nitrogen loss can be battled through one of two ways; place the urea two inches deep in the soil, or apply nitrogen that has been coated with a urease inhibitor. Floating on nitrogen coated with a urease inhibitor allows nitrogen to be in the soil in the spring with minimal loss making fall application of nitrogen a viable option for farms of all sizes.
The urease inhibitor slows the rate of hydrolysis and controls the pH levels of the soil. This also then allows moisture to move the urea down into the soil and prevent the release of ammonia into the atmosphere. The use of a urease inhibitor can minimize nitrogen losses to 10% as compared to the 50% potential loss of nitrogen with untreated urea.
One product available for fall application of nitrogen fertilizer that will aid in minimizing nitrogen loss is SUPER U™ granular fertilizer. SUPER U™ fertilizer is a finished stabilized fertilizer product that contains both a urease and a nitrification inhibitor to protect nitrogen against denitrification, nitrate leaching, and ammonia volatilization. It contains the highest concentration (46%) of nitrogen available in a stabilized granular fertilizer that protects against all three forms of nitrogen loss.
There are other reasons that make fall application of nitrogen and sulfur a beneficial practice. Fall fertilizer prices are generally lower than they are in the spring creating a financial benefit as well. Floater operators, if floating is the option needed, have more time in the fall than they do in the rush of seeding creating a timing benefit. The fertilizer can be stored in the ground rather than tying up bin space with fertilizer. Applying nitrogen and sulfur in the fall so only phosphate and potash need to be applied in the spring means less hauling product to the field, less stop time to fill during seeding, and it will free up your air tank allowing you to seed more acres in a day. The spring is loaded with many pressing jobs so it helps to have one job taken care of in the fall once harvest is complete and things slow down around the farm.
As we all know, spring weather is unpredictable so knowing your land will help minimize losses from a fall application of fertilizer. Fields prone to flooding may not be viable option for this application. Flooding may wash product away, and if the fields are too wet in the spring, product may also be lost if seeding is delayed.